Note: Descriptions are shown in the official language in which they were submitted.
61~
B~CKGROUND OF THE INVENTION
The present invention relates to the method and
apparatus for controlling defrost and refrigeration opera-
tions in a refrigeration system having a plurality of
evaporators. More particularly, the invention relates to
controls allowing the evaporators to be defrosted and re-
frigerated independently and without overloading the sys-
tem. The invention has utility in refrigeration systems
having hot gas or other defrosting equipment.
It is customary in large refrigeration systems
such as found in food stores or supply houses to utilize
an integrated refrigeration system for a plurality of
refrigeration units. A common compressor and condenser
supply all of the refrigerant needed by the evaporators in
the various units. However a certain degree of independen-
cy of the units is required because of the different demands
imposed on the units. For example, in a food store, a re-
frigeration cabinet containing ice cream or frozen foods is
normalIy held at approximately -20F and imposes far more strin-
gent demands on the refrigeration system than a milk cabi-
net or veget~ble tray that operates in the vicinity of +40F.
Furthermore, temperature and humidity conditions and the
frequency with which the cabinets are opened and closed at
various times of the day also affec~ the refrigeration pro-
cess. Because of the variations in demand, the accumulation
of ice and frost on different evaporator coils in the system
varies widely, and independent defrosting and refrigeration
controls are needed to keep the evaporators and the system
operating efficiently. In this respect, reference to an
evaporator is intended to refer to one or more evaporator
coils connected in parallel or series to be refrigerated
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and defrosted in commo
¦ In large con~ercial refrigeration systems, defrostin~
is -frequently accomplished by transmitting hot refrigerant in
Igaseous form d;rectly through the evaporators to melt the
¦accumulated ice and frost. Such hot gas defrosting s~stems may
'reduce the available refrigerant for cooling purposes to an
inadequate level for other evaporators in the system unless control~
is e~ercised over the number of evaporators that can be placed in
the de-frosting mode at any one time. Also ~vith other defrosting
~devices such as electrical heaters connected to the evaporator
coils, the number of evaporators defrosted at any given time must
be controlled to prevent power overloads and undue demands on the
refrigeration equipment.
~5 I Accordingly, it is customary in refrigeration systems
~having multiple evaporators to limit the number of evaporator~ that
are placed in the defrosting mode at any given time - Such limita-
. Itions can be imposed by scheduling the defros$ operations -for
particular times of day, ho~Yever, timed defrosting may not be
satis~actory where demands on the refrigeration system are
¦irregular and incapable o~ prediction. In these cases, a demand
~defrost system is generally preferred. In a demand system, frost
sensors associated with the evaporators provide signals ~Yhen
accumulated frost and ice has reached a given level. In the
Iabsence o-f further control, however, it is clear that a demand
syDtem could place nlOre than one and possihly all of the
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evaporators in defrost at one time. To prevent the possi-
bility, control systems, have been devised such as disclo-
sed in U. S. Patents 3,894,404 and 4,151,722. Tn U. S.
Patent 4,151,722, scanning means are provided to periodi-
cally interrogate or examine the frost sensors in a prede-
fined sequence. When one of the sensors indicates that its
corresponding evaporator is in need of defrost, scanning is
halted until defrost of the evaporator is complete. A
certain priority can be developed by increasing the fre-
quency that one evaporator is scanned relative to theothers. Thus, for example, a high priority evaporator can
be scanned twice as often as the other evaporators to in-
crease the probability of detecting the need for defrost
at an earlier point in time.
It is an object of the present invention to provide
a defrost and refrigeration system which allows a plurality
of evaporators to be controlled independently of one another
and which constitutes an improvement ov~r the prior art
systems.
SUM;l~RY OF THE INVENTION
In accordance with one aspect of the present in-
vention there is provided a control apparatus with a
refrigeration system having a plurality of evaporators and
defrosting equipment connected to defrost each of the eva-
porators independently of the others, comprising timing sig-
nal generating means having an adjustable speed for produ-
cing at an adjustable rate timing signals from which the
defrosting of individual evapoxators are scheduled, control-
led switching means connected between the timing signal
generating means and the defrosting equipment for actuating
in response to the timing signals individual portions of
the equipment associated with the respective evaporators
and thereby switching the corresponding evaporators into a
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defrosting mode when a timing signal for said evaporator
is produced, and testing means connected in controlled
relationship with the timing signal generating means for
increasing the rate at which the timing signals are gene-
rated and for thereby switching the evaporators into their
defrost modes at accelerated points of time.
In accordance with a further aspect of the pre-
sent invention there is provided a method of testing the
defrost controls in a refrigeration system in which a plu-
rality of evaporators are scheduled to be defrosted at dif-
ferent times in response to defrost signals generated by a
time clock, comprising driving the time clock at an accele-
rated rate at least until the clock reaches a time when a
given evaporator is scheduled for defrosting and a defrost
signal for the given evaparator is generated, and determi-
ning if the defrost signal for the given evaporator is
generated at the scheduled time.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram illustrating the
overall refrigeration system having a plurality of evapo-
rators with individual refrigeration/defrost controls for
each evaporator.
Fig. 2 is an electrical diagram illustrating the
various components in the master control for the refrigera-
tion system.
Fig. 3 is a diagram of a digital time clock and
decoders which generate time signals for the refrigeration
system in one embodiment.
Fig. 4 illustrates in greater detail one of the
numeral elements utili~ed in the digital display of the
time clock in Fig. 3.
Fig. 5 is a block diagram illustrating the
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functional elements of an individual refrigeration/defrost
control and connections with the master control of Figure 2.
Fig. 6 is divided into Figs. 6A and 6~ as shown,
and constitutes an electrical diagram illustrating a solid
state embodiment of the individual refrigeration/defrost
control in Fig. 5.
Fig. 7 is an electrical schematic illustrating
the power supply for the digital time clock and the defrost
controls.
10DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 illustrates the components of a refrigera-
tion system, generally designated 10, embodying the present
invention. A compressor 12 delivers hot, gaseous refrige-
rant to a cond~nser 14 where heat is transferred to the am- `
bient air with the aid of a cooling fan 16. Cooled and
condensed refrigerant is directed in a conduit 18 from the
condenser to evaporators 30, 32, 34 by refrigeration and de-
frost control valves 20, 22, 24 respectively when the valves
are individually set in the refrigeration mode. When the
valves are set in a defrost mode, the compressor 12 supplies
hot refrigerant in gaseous form to the respective valves and
associated evaporators through the conduit 36. The conduit
37 returns the refrigerant to the compressor. A more detai-
led description and explanation o the refrigeration and
defrost valves may be had from the above reference U. S.
Patent 4,151,722.
The refrigeration and defrost operations or cycles
for the plurality ~f evaporators 30, 32, 34 are controlled
by a master control 38 associated with all of the valves and
evaporators, and individual refrigeration/defrost controls
40~ 42, 44 connected separately and independently with the
-respective valves and evaporators. Thus, the individual
control 40 regulates the flow - -
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of condensed or hot re~rigerant tllrough the valves 20 and
¦ evaporator 30, the individ~lal control ~2 regulates the ~low o~
condensed or hot refrigerant through the valves 22 and evaporator
1 32, and the individual control ~ regula-tcs the flow of re~rig-
I exant through the valves 24 and evaporator 34.
From the above description, it will be understood that ¦
the'refrigeratlon system 10 has a hot ~as defrosting system to
i defrost the evaporators 30, 327 34 individually. However, the
¦ present invention is not limited to a hot gas defrost system and
! other types of de~xosting equipment s~ch as electrical heaters
can be connected respectively with the evaporators to permit
¦ independent defrosting'of the separate evaporators.
¦ The master control 38 in Fig. 1 i5 illustrated in a
I solid state embodiment in Fig. 2. Among other ~-lnctions, the
' I master control provides time sigllals that allow the individual
¦ refrigeration/de~rost controls to operate on a timed basis. The
control 38 also provides the mealls by ~vhich testing of the indi--
¦ ~idual controls can be accomplished, and includes a unique
, scanning device that allows the evaporators to be interrogated'
, concerning the need for de~rosting in order o~ priority.
, ' IME DECODING
' In Fig. 2, the basic source of time signals in the
mas~er contr~l 38 is the digital time clock 50. ~Yhile the
~ digital clock is not essential to many aspects o~ the present
2s 11 inven ion, it does provide e unique means by which time signals
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j can be generated. In one form, the digital clock is a 24-hour
clock having a digital display and by means of a two-hour decoder
¦ 52 and a 24-houl decoder 54, a time signal is produced every half
¦ hour. Thus, any one of the evapor~tors in the re~rigeration ¦-
I system can be scheduled in the timed mode.to defrost at any hour
or half hour of the day. Although an evaporator may be scheduled
to defrost at a particular time of day, such defrosting ~vill not
necessarily occur due to the defrosting of higher priority
evaporators as described in grea-tex detail below.
In ~der to more fully understand the operation of the
.. I time clock 50 and decoders 52 and 54, reference is made to Figs. -
3 and 4. The digi-tal clock 50 has counter and control circuitry 5
which is enexgized by 60 cycle a.c. power. The circuitry utiliz- 1
. ing the 60 cycle power as a timing reference computes time which I :
is pre~erably output in BCD form to four 7-segment decoders 60,
. 1 62, 64, and 66. The 7-segment decoders are associated respective-
. I ly with numeral elements 70, 72, 74, and 76 that ~orm the digits
........ ¦ o~ the time clock display and each decoder generates one of the
! time digits. For example, the decoder 60 generates the tens-hour
.20 I digit, the decoder 62 generates the ones-hour digit., the decoder
, 64 generates the tens-minute digit and the decoder 66 generates
the ones-minute digit. For the purpose of discussion, it will
I be assumed that the digital clock is a 24-hour clock such as model¦
.: I ~i~1002 digital clock module manufactured by National Semiconductor
.25 Corporation, Santa Clara, California. Each numeral element 70,
.; ¦ 72, 74, and 76 has the same construction shown ill Fig. 4 and com-~ prises a circuit board 78 havin~ seven liglt emitting diodes
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(LED)s or segments A, B, C, D, E, F, and G arr~n~ed in a
figure-S pattern. Any decimal intcger Irom 0 to 9 can be
illustrated in the pattern by illuminating selected segments in
¦ combinatio~, and it ~rill be assumed that the segments are con-
j stantly energized when illu3ninated to form a particular integer.
By energizing selected s-egments in various combinations and
patterns in each of the numeral elcments, a visual presentation
of the time is manifested. The display changes everyrninute in
accordance with the data produced by the counter circuitry ~
Since the excitation of the segments and the corres-
ponding illumina-tion is peculiar to a given time, a time signal
can be generated by determining which sevments are illuminàted
at that particular time, then moni-toring the energi~ation or
illumination o~ the segments and producing the time si~nal when
the particular combination or code of illuminated segn~ents is
Aetected. It is not essential that all illuminated segments
¦ be used to establish an unambi~uous code. Only some of the
I illuminated se~ments may be uniquely associated with a particular
¦ time. When signals are desired at spaced times thxoughout a day,~
I particularly evenl~ spaced times when a digital integer is
¦ r~peated, it is frequelltly possible to ~e~nelate a time signal from
less than all illurminated segments. Furthermole, the non-illumin~
I ated segments or combinations of illuminated and non-illuminated
j segments may provide a unique time code. It is also possible
ithat the code b~ based UpOll derivative parameters of the digital
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display such as positive-going or negative-going transitiOnS of
the segments between the ener~ized and non-energized conditions
Accordin~ly, a unique time si~nal generatinD ~n~ans is provided by
! decoders such as the decoder 52 which monitor the energizatiOn
I of a digital display and produce signals whell a predetermined I -
¦code is detected. By counting or accumulating the time sigllals,
further time interval signals can be obtalned.
It can be shown by analysis o tlle illumination patterns¦
I that the B and C segments or LEDs of the tens-minute digit when
lapplied to a coincidence gate, such as the AND gate 120 in the
decoder 52 of Fig. 2, initiate a positive pulse on the hour and
¦half hour corresponding to a freq-lency of two cycles per hour.
For digital circuitry, such a cyclic rate is very low, but the
resolution provided by time signals generated at tllat frequency is
~5 ladequate for selecting defrosting times. The pulse signals are
used as clock inputs ~or a solid state "D"-type flip-flop 122 and j
a static sllift register 124 which serves as a sequencing and accu- j
¦.~! Imulating means. Both the flip-flop and shift xe~ister respond to
Ithe leading edge of the positive pulses, and cause the outputs 80,
!0 ¦82, 84, 86 to se~uentially assume a binary l-state or "high" with
!each succeeding pulse. Thus, every half hour the outputs chanve to
¦Igenerate a time signal and only one O~ltpUt iS in the l-state or
` ! tuxned on at any given time. One half-hul a~ter the output 86
; ~,is turned on, the leadillg edge of a subsequent pulse from th2 ~N~
;5 gate 120 causes the sequencing of the output signals to be started .
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¦ again througll the feedback connection ~ith the "D" input of the
¦ ~lip-~lop 122. Thus, -tlle four outpUts 80-86 of the two-hour
decoder are tuxned Oll individually and at evenly spaced inter-
i vals over a two-hour pexiod. The flip-flop and shift register
¦ ef~ectively count the timing pulses produced by the coincidence
¦ gate 120 so that the outputs of the decoder provide not only
time signals but signals representing accumulated time in ha~
hour increments over a two~hour period as illustrated.
At the end o~ a t~Yo-hour period, when the output ~0 is ¦
again turned on, the leading edge o~ a pulse ~rom the output is
¦ transmitted to another "D"-type flip-flop 126 and a shi~t reg-
¦ ister 128 which comprise the 24-llour decoder 54. The shift
: register 128 is illustrated as a single shift register, but in
~act, could be comprised o~ a plurality o~ shi~t registers
connected in series. The operation of the ~lip-~lop 126 and ¦ -
.; shift register 12S is basically the same as the ~lip-flop 122
;~; and sh~t register 124 except that since the clocl; signals are ¦
s j derived from the decoder 52, the outputs 90-112 are turned on
J individually in sequence at 2-hour intervals. ~Yith twelve such !
¦ outputs, a time signal is produced ~rom the decoder 54 every
` ¦ 2 hours over a 24-hour period. By applying the time signals from
I the outputs o~ both decoders 52 and 54 in various combinations
Y; ! to coincidence ga~es, a time signal can be pxoduced at any
I hal~ hour of the day over a 2~-hour period.
For purposes o~ setting the shi~t registers 124 and l~S
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a reset circuit 130 is provided. The leset circuit is basically
¦another decoder connected with the digital clock 50 and is
; Icomprised of a NOR gate 132. ~s indicated, the inputs to the
gate 132 are ta~en ~rom the B scgmellt of the ten hour digit,
the C segment of the hour digit, the G segment o~ the 10-minute
digit and the C segment oP the minute digit. Due to the logic
f of the NOR gate, a positive pulse is initiated and applied to the
~lip-~lops 122 and 126 and the shift registers 124 and 128
lonly when none of the identified segments serving as inputs
is energized. Thus, the NOR gate fùnctions in respo~se to the
i Inon-energization of selected inputs, and it can be shown that ¦ -
¦with the identified inputs and associated code, the NOR gate pro-
duces a positive one minute pulse at 2:02 witll a 24-hour clock.
~ A second but inconsequential pulse occurs at 2:12. In response
`1 15 to the leading edge of the first pulse, the outputs of
^ !decoders 52 and 54 are set independently of clocking pulses and
¦the outputs assume the states correspondlng to the time 2 02.
f~ ISuch setting function is used to s~nchronize the outputs and the
¦time display of the clock a~ter the system is turned on.
~ From the above, it ~ill be understood that the time or
,timing signals for initiatillg defrost operations are derived i-
¦from the digital clock 50 by the decoders 52 and 54. Although the ¦
!signals are generated in half hour increments by the exemplified
¦~ Icode, other codes utilizing both ener~ized and non-energized
'segments permit many other time increments and timing si~nals to
be obtained.
~hile the digital time clock 50 and decoders 52 and 54
rcpresent a unique means for obtaining time signals, the
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; refrigeration system could also oper~te with more conventional -
i timing devices providing signals at selected times o~ day.
¦ Also, the illumination o-E numeral segments from which the de-
~ codels operate can be derived from timing devices other than
I the digital clock. Still further, it is contemplated that -
¦ energization of numeral element5 other than the seven segment
numerals may be monitored to produce time signals.
:~ TE~T FUNCTIO~
The master control 38 includes components for tes-ting
0 ¦ an individual refrigeration/defrost control for an evaporator. ~i
A test ~unctlon is carried out by progran~ing an individual con-
¦ trol ~0, 42 or 4~ in a time defrost mode of operation and then
driving -the di~italclock at an increased rate until the time is
` ~ reached when the individual control under test is pro~rammed to
` 15 , initiate a defrost cycle. The control is then examined to deter-
1~ ¦ mine i~ a de~rost operation has been properly initiated.
In particular, a NOR ga*e 140 has one input terminal
~ that is normally held in the l-state by the power supply and
¦~ a resistor 142 and another input held in the 0-state by the
1I power supply, resistor 136 and digital inverter 138. When a ¦
I' test signa1 as illustrated in the foxm of a negative or "low
¦~ level signal is reccived rom any of the individual defrost
- 1 controls ~0, 42 or ~4, the signal switches the output of the
NOR gate to its l-state, provided that a defrost signal is not
!~ present at the other input terminal of the gate. A defrost
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- signal,also illus-trated as negative si~llal, indicates $hat one of
the individual controls and a corrcsponding evaporator is in a
defrosting cycle, and inhibits the NOR gate l40 and test function
ndex such circu1nst~nces to prevcn-t more 1;11an o11e evaporator fl~.n
being placed in a deflosti11g mode at a time. It should be noted
! parenthetically that the oval designations in the dra~vings repre- i
: ~ sent conductors that are common to all of the evaporators, and
therèfore, the test signal or defrost signal may come from any
. I one Or the individual defrost controls 40, 42? ~. A defrost
; lO signal is also applied to a "D" valve 1~4 which reduces the com- ¦
pressor discharge pressure so tl1at hot ~as from -the compressor
can be circulated through the evaporators in a hot ~as defrosting ¦
system.
Assuming that a defrost operation is not being carried
`15 ¦ out when the test signal is received, the output of the NO~ gate
140 is transmitted through an OR gate 1~6 to ~ast clocking cir-
cuitry 1~8 in the digital clock 50, and the digital clock is then ,
driven at an accelerated rate. For example, the digital time
j display is sequenced through one hour in an actual time of one
~0 second. Since the decoders 52 and 5~ respond to the display
xather than actual time, the time signals produced by the outputs !
; of the shift xegisters 124 and 128 appear a$ a correspondingly
accelerated rate and the programmed time of defrost for a ~ar-
¦ ticular evaporator is reachecl in s11ort orc1er. As soon as the
25 j individual control under test xeceives its progra~1ed .time signal,
`~ !
-.~ I the control should go illtO the deIxost mode of operation a1~d a
.~ defrost signal should be transmittcd from the Ul1it under test to ,
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the NOR gate 1~0. The NOR ~ate lg0 is then disabled $ogeLher
with the ~ast clocking circuitry l~S and tlle digital clock xe- i
turns to normal time sequencin~. By observing the digital dis- j
¦ play o~ the clock, the operator conducting the test can determine
I i~ the tested control is ~unctioning properly.
¦ As explained in greater detail below wi-th re~pect to the
individual defrost controls, the -test operation will continue
until it is terminated by the operator. Termination of the test
also terminates defrosting o~ the tested evaporator so -that
I the de~rost signal disappears and the NOR gate 140 reverts to its
initial condltion.
Since the test ~unction drives the digital clock to
the time ~hen the tested evaporatox contxol is programmed for
¦ defrost, the termination o~ the test ~unction will normally
lS ¦~ leave the digital cloc~ at the wrong time. For this reason, the
operator who xan the test should reset the clock to the correc$
time, and ~or this purpose, a ~ast clock setting button 152 and
a slow clock setting button 154 are provided. The fast button
1 152 actuates the fast cloc~ing circuitr~ 148 through the O~ gate
-~ 2~ ¦ to bring the digital clock approximately to the correct time~
The operator then presses the slow button 154 ~vhich actuates the j
slow clocking circuitry 156 to drive the cloc~ at a xate much
less than tlle ~ast clocking cixcuitry but sliglltly greater than
, real time. The slow button is rcleased ~/hell the corxect time
is observed on the digital display.
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It ~ill be noted that whenever the time clock 50 is
being set during testing or by either the fast or slow buttons
152 and 154, OR gate 150 produces a clock setting signal. The
setting signal is used as described hereinafter to disable or
lockout all individual defrost controls other than the one
under test. The lockout function is necessary because the
decoders 52 and 54 continue to respond to the digital display
as the clock is set, and the generated time signals may
correspond to the programmed times for which certain evaporators
other than the one under test are scheduled to defrost.
Accordingly, testing of the individual defrost controls
40, 42, 44 is performed by driving the time clock at a high
rate until the programmed time appears in the digital disp~y.
Clocking stops at that point and a defrost operation is actually
carried out until the operator decides to terminate the test. ~-
Thereafter, he resets the clock and the timing signals are
; generated in correspondence with the actual time of day.
:.
SCANNING FUNCTION
As described above, it is desirable in a refrigera-
tion system having a plurality of evaporators to limit thenumber of evaporators which can be placed in the defrost mode
at any one time in order to minimize power and cooling capacity
overloads. It is especially desirable in hot gas defrosting
; systems to limit the number of evaporators in defrost in order
to appropriately scale the capacity of the refrigeration com-
pressor 12. In ...
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the present embodiment, only one evaporator is defro5ted at
a time but higher limits are certainly feasible. ~ccordingly,
the master control of the present invention is provided ~vith a
~ priority scanner 160 ~Yhich produces sequential probing signals on ,
I the outputs lG2-176. The probing signals are used to interrogate ¦
, the evaporators or the individual controls fox the evaporators in
regard to the need for de~rost. In per~orming the interrogation
function in one embodiment of the present invention, the probing
signals e~ectively serve as ~ating signals and aliow an indivi-
¦dual control to initiate defrosting of the associated eVApOratOr
I when the need is indicated. I~ this respect, the need is shown
to exist by a signal ~rom a ~rost SellSOr connected with an evap- ¦
orator or by a programmed time signal generated by the decoders
52 and 54.
The priority scanner 160 is driven by clocking pulses
~from a clock pulse generator 180. The p~lse generator receives
; jstandard 60 cycle a.c. current and produces a clocking pulse every .
3-75 seconds or 1/16th of a minute. The priority scanner 160
receives the pulses on a clocking input vJhich triggers the outputs
162-176 one at a time and in n-lmbered sequence. One output is
l turned off and the next output is turned on with each positive
.~ transition of the clocking pulses, and when each o~ the eight
~outputs has been triggered, the sequence is repeated in a cyclic
,fashion. Thus, with eight outputs and clocking pulses every 3.7~ j
, 25 ~seconds apart, eight different evaporators associated respectively
. iwith the eight outputs can be scanned by the probing signals in a
pcriod o~ 30 seconds.
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The priority scanner 160 in one form can be an
integrated circuit such as an RCA counter/divider 4022.
The circuit resets and holds the scanner on the highest
priority output when a l-state signal is applied to the
reset terminal.
Scanning a plurality of evaporators to indentify
those in need of defrost is disclosed in U. S. Patents
~,894,40~ and 4,151,722. ~owever, the scanner 160 performs
the scanning function on a priority basis by always resuming
0 the scanning function when interrupted with the first pri-
ority output 162. Thus, by connecting the most important
evaporator with the first priority output and other evapo-
rators with the other outputs in order of priority, the
more important evaporators and refrigeration cabinets are
~- defrosted before the others.
Such prioritizing of the defrost operations should
be distinguished from the prior art systems shown and des-
cribed in the referenced U. S. Patent 4,151,722 wherein
certain evaporators are interrogated more frequently than
other evaporators. In the present system, a definite prior-
; ity is assigned to each evaporator to ensure that the highest -
-~ priorit~ evaporators will be defrosted first. Furthermore,
the order of priorities is observed regardless of the stage
of the scanning se~uence when scanning is interrupt d.
In the present system, the scanning is interrup-
~ ted at several junctures. Since no more than one evaporator
,.: ,- .
is placed in a defrost cycle at a time, the defrost signal
applied to the NOR gate 140 is also transmitted through an
OR gate 18~ connected with the reset input of the scanner -~
160. Regardless of which
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evaporator is producing the de~rost signal, sc~nning is stopped
I and ceases as long as the defrost signal holds the output o~ the
¦ 0~ gate in the l-state. ~hen the defrost cycle terminates and
the defrost signal is removed from the OR gate 182, the scanning
function xesumes with the ~irst priority output 162 either imme- ¦
diately or, if a switch lS8 is closed, a~ter'a short delay
¦established by a delay timer 190. ~Yith the switch 188 closed,
~" the timer responds through a capacitor 192 to termination of the
defrost signal and transmits a delay signal through OR gate 182
' 10 which delays th'e resumption o~ scanning and allows the system to
~" recover from the previous defrost cycle and balance out in pre-
para$ion ~or the ne~t cycle. Thus, if de~rost o~ the evaporator
connected with the fourth priority output 168 has just been com-
pleted and the evaporat~rs connected with the second priority out-
put 164 and the sixth priority output 174 are both in need of
defrost, the scanning operation first picks up the second priority
¦evaporator rather than the sixth priority evaporator. There~ore,
the higher priority evaporators are cIearly given pre~rence.
The priorlty scanner 160 is also reset in several other
linstances. When either the ~ast clocking button 152 or the slow
~ Iclocking button 154 is pressed, a triggering signal is applied to
: jone o~ the inputs o~ t~e OR gate 182 to reset and hold the
¦scanner until the time clock 50 is set. Thus, with a new time
¦in the display, scannin~ restarts with the highest priority '
~25 levaporator. It ~Yill also be understood that ~henever one of the
individual de~rost controls is'tested, the time clock is set and
~a defrost signal resets and holds the scanner until the test is
, I ,
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,,,
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.:
3~i7
¦ terminated. Scanning again resumes ~vith t~ highest priority
~;~ I evaporator. ~dditionally, a fourth inp~lt to the OR gate 182 ~rom !, the t~Yo-hour decoder 52 is moment~rily pulsed by the t~vo-hour
decoder 52 through the capacitor 18~ alld rosets the scanner at
;; 5 the end of each two hour interval when the time signals from the
24-hour decoder change. Resetting at this juncture synchronizes 1,
the start of scanning with the start of a new timing period. In
. this ~ashion, it is possible to schedule some or all of the
evaporators fox defrost at a given time of day, for exalllple, 3:00
a.m. When the 3 a.m. signal is generated~ the scanner 160 is
I a~utomatically reset and the scheduled evaporators are de~rosted
; j one at a time in order of priority.
Accordingly, the priority scanner 160 interrogates the
plurality of the evapola-tors concerning the need for defrost and
gives preferance to those evaporators connected with a llighex
priority output of the scanner. The scanning function with
priority may be utilized when the evaporators are programmed to
defrost in either a time mode as described above or in a demand
mode where, for example, a plurality of frost sensors simultaneous-~
ly indicate a need for defrost;
INDIVIDUAL DEFROST CO~T~OL
Having described the master control 38 in detail,
' reference is now directed to the individual refrigeration/defrost
,.. ~ , . . .
controls ~0, ~2J 4~. An individ~lal control is provlded for each
¦ ~vapoxator that is to be refrigerated and defrosted indepelldently
',' I - ' I .
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. ~ I .
.,. .. .
3 Z ~J~
~,f the others. Although three such evaporators and correspond-
ing controls have been shown in Fig. 1, any number of evaporators
~ can be integrated in a refrigeration system providing that the
- compressor and other components have an appropriately scaled
capacity. Since each individual control has the same construc-
tion and functions in the same manner, only one such control is
described and shown in Figs. 5 and 6.
Fig 5 is a functional diagram of the individual
defrost control 40 for the evaporator 30 and illustrates the
connections with the master control 38 and other individual
controls.
' The basic inputs to the individual control 40 are
received by a time and mode selection circuit 200. Time signals
are received by the circuit from the two-hour decoder 52 and the
24-hour decoder 54. Scanning signals when desired are also
` applied to the circuitry 200 from the priority scanner 160 and
a frost signal may be provided from a frost sensor 202 connected
with the evaporator 30 associated with the individual control. ~-
The frost sensor may be of the type described in U.S. patent
3,453,837 which provides a signal indicating a need for defrost
when the temperature differential of air blown through the ;~
evaporator indicates that defrost is needed. Of course, other
types of frost sensors providing a frost signal can be utilized
in the present invention with equal facility.
The time and mode selection circuit 200 is designed
to allow defrosting to occur either on a timed basis with signals
: `
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¦ received from the decoclers ~2 and 54 or a demand basis with a
signal received frolm, the sensor 202. The programming of the cir- ,
; cuit determines precisely ~vhich mode of operation is employed and
¦ in a preferred embodiment the mode can be s,elected at will. 17hen
~ the priority scanner 160 is utilized to establish priority of -
" , de~rosting among several different evaporators, a defrost actuatin~signal ordered on either a timed or demand basis is not trans-
mitted by the circuit 200 until a discrete probing signal from the'
, i scanner is received. When the defros-t actuating signal is ordered
,, I
~10 I by any means, the selection circuit 200 transmits the signal
,, ¦ through a two hour latch circuit 204, a defrost lockout circuit
¦ 206 and a clock lockout circuit 20S to a defros-t control s~vitch
210. The control switch 210 is preferably a solid state switch
¦ which can be set and reset by di~ferent sig-nals. ~rhen the signal
, from the selection circ~itry is received, the contlol s~vitch 210
¦ actuates a refrigeration valve or valves 212 and a defrost valve
or switch 216 through an unlatching circ~itry 214. The valve
212 closes and stops the fclow of liquid refrigerant from the '
~ ! condenser into the evaporator and thusly terminateS coc>ling of
;Z0 ¦ the evaporator. The refrigeration valve is also connected with
,` I a xefrigeration indicator 21S such as a light that is turned off
when the refrigeration valve is closed.
~- I In a hot g~as defrost system, the clefrost valve 216 opens
' ! at substantially the same time that the refrigeratioll valve closes,
" I and admits hot gases into the evaporatox in orcler to melt ice and
" frost accumulated on the evaporator coils. Nhen the valve 216
.:, . ' ',
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326'î~
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i opens, a defrost indicator associated with the valve is turned on
Since the indicators 218 and 220 are associated only with the
evaporator 30 in the group of evaporators defrosted and re-
~ ~rigerated by the compressor 12, reference to a display panel or
~ circuit containing the indicators will immediately show what
I cycle the evaporator is in.
It should bè understood that the defrost valve 216 in
- another embodiment o~ the refrigeration system may be a switchin
device which controls the ~low of current in the electrical de-
! frost heater connected with the evaporator 30. Thus, the inven-
j tion is not limited to the hot gas defrost system but has general
applicability to refrigeration systems having a variety of de-
I frosting means.
i I If the timed defrost mode has been selected for the
I evaporator, the two~hour latch circuitry 204 effectively prevents
¦ the associatcd evaporator rom being defrosted again within the
; I two-hour period in which deIrosting was originally ordered. Since
; I the time for defrosting an evaporator is usually less than two
j I hours, it is probable that a programmed time signal ~or the evap-
~; 20 I orator will still be present at the input of the selection cir- ¦
cuit 200 when the defrosting cycle ends. Therefore, upon resump-
¦ tion of scanning the higher priority evaporators, defrosting of
the same evaporator would be repeated without reaching the lower
i .
s priority evaporators if the t~o-ho~lr latch circuit were not
I employed.
Thc defrost locl~out circuit 206 receives a defrost
signal from any of the other evaporators which îs in a defrosting
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cycle and prevents the evaporator 30 associated with the lockout
circuit 206 from also being placed in the defrost mode even if
; I a time or frost signal indicates a need for defrost. Accordingly,I only one evaporator in the re~rigeration sys-tem can be defrosted
¦ at a time in response to a defrost signal.
¦ The clock ~ckout circuitry 208 prevents a defrost opera-j
¦ tion from being initiated by a defrost signal whenever a clock s
setting signal ~rom the master control is received. Thus, during
¦ testing of other evaporators in the refriger~tion syste~ the time
¦ clock is driven at an accelerated rate and may reach the pro-
grammed time for de-frost of the evaporator 30 connected with
¦ the loc~out circuit 20S before the prograinmed time for defrosting
the evaporator ~nder test. The lockout circuit disables the de-
¦ frost signal from circLIit 200 and ensures that only the tested
¦ evaporator goes into the defrost mode. The lockout circuit 208
; I also prevents the individual control 40 from responding to the
time signals whenever the time clock is being manually set.
A manual de~rost button 222 is connected with the defrost
.,
control switch 210 to initiate a defrosting operation independent-
ly of the decoders and sensors connected with the selection
circuit 200. Since the button has a direct input to the control
switch 210, a normal defrosting operation is carried out when the
button is pressed regardless of the condition of the latching and
,i I lockout circuits 204, 2061 and 208; therefore, the circuits can
--25 I be overridden by the man-lal defrost button and more than one
j evaporator may be placed in defrost if necessary.
': I . i
~ ~24- '
. . !
I . . !
The individual control 40 is provided with a tes-t
:~; !button 224 to test the operation of the con-trol and the associated ,
,portion o~ the ~aster control 38. To perform the test function~ it,
is necessary that the time and mode selection circuit 200 be pro- '
5 ¦grammed in the time mode with the evaporator scheduled to begin ',
la defrost operation at a paxticular time. When the test button 224-
¦is $hen pressed, a test ~unc-tion signal is transmitted from the
individual control ~0 to -the master control where,- as described
above in the absence o~ a defrost signal from any o~ the other
~evaporators, a fast clockiI1g signal is generated, and the digital
`, Itime cloc~ is driven at an accelerated rate... When the scheduled , -
~time of defrost for the individual control 40 is reached, a defros$~
~ !actuating signal emanates from the circult 200 and defrosting starts
`; ¦in conventional fashion. -¦
lS I It will be observed in Fig. 5 that the test function sig-~
~ !nal within the individual control 40 is applied to an inhibit cir-
,.~ ~cUit 226 interposed between the master control 3~ and the clock lock-
¦out circuitry ~0~. The inhibit circuit prevents the clock setting J
,signal generated in the master control 38 from enabling the clock
¦lockout circuit 208~ and thUs as the time clock iS drive~ a$ an
- laccelerated speedJ a defrost actuating signal derived ~rom the
~; Idecoders 52 and 54 is transmi tted from the selection circuit 200 to
the defrost control s~vitch 210 to initiate the de~rost operation.
In summary, when the test button 224 is pressed, the $ime
,clock 50 is driven at an acoelerated rate until the scileduled time '
for defrost o~ the individual control 40 is reached, and the de- j -
¦~rost operation is initiated. Even if -the scheduled ti~nes of the
~ other evaporators 3~ and 44 are traversed, the other individual con-
,, . .
,~ jtrols 42 and 44 associated with o ther evap~rators will not initiate;
ide~rost operations due to the clock lockout circuitry in the other
individual controls.
When defrost contlol switch 210 is ac-tuated by the
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de~rost actuating signal, the re~ eration valve 212 is closed
and the xefrigeration indicator 21~ is turned o~f. At the same
time, the de~rost valve 216 Ol valves ale actuated to admit
hot gas to the evaporator or other~Yise apply heat to the
~ evaporator, and the de:Erost indicator 220 is turned on. It will
.~ I be understood that the indicators 218and 220 within the individual
l ¦ control 40 only re~lect the mode o~ operation o~ the evaporator 30
¦ associated with the control. Thus, the person rullning the test
: ¦ can visually determine ~rom the indicators whether the master I .
..; 10 ¦ control 38 and the individual control 40 are operating properly.
¦- As long as the test button 224 is pressed, the defrost
.. operation will continue in its normal fashion. A de~rost signal
... ~rom the control switch 210 is transmi-tted to the defrost lockout ,
r circuitry 206 as well as the master coutrol 3S and the other in- j
. 3 dividual controls 42, 44, etc. ~y holding the test button 224,
:- a ~ull de~rost operation can be carried out and then terminated
in normal ~ashion as described in greater detail below; hou/evex,
i in most instances, the test button 22~ is only held for a brief
period of time until the re~rigeration indicator 21~ and defrost
j indicator 220 have turned o~ and on respectively. The operator
~ ! has then received all in~ormation necessary to establish that
. ,
. , the controls are properly operating aud at -that point he ~uld
. ,
I release the test button 22~. Upon release, the test ~unction
~ I signal terminates in the inhibit circuitry 22~, the master con-
25 I trol 38 and other individual c~ntrols 40, 42. ~t the same time,
', ' ', . ' .
',' I .
:
I 11 3Z~7~ - -
.~ ~ a reset signal is transmit-ted from the button to the de~rost con-
trol s~vitch 210 whicll resets the re~rigeration valve in the open
position and closes the de:erost valve 216 by way of the unlatch
¦ circuitry 21~ The operator observes that the refrigeration indi- !
cator is turned on,-and the de:erost indicator is turned o~f and
thereby verifies that tlle evaporator has returned to a refrigera- ~
tion cycle ~ollowingthe test~ The time clock 50 must then be re- ¦
set to the corxect time by mealls of the setting buttons 152, 154
~ in the master control o~ ~ig. 2.
`~.10 I DEFROST T~MIN~TION
A time or demand defrost cycle, ox a test cycle if the
test button is held for the full duration of a de~rost cycle,is
I terminatecl in one of three methods. In the first method a thermo- !
I stat 230 ox other sensor on the evaporator 30 associated with the
I indivi~lal contlol ~0 sends a defIost terminate signa~ to the
¦ unlatching circuit 214 to cut off the actuating signal for the
de~rost valve 216 and allow the valve to close or shut.o~f other
heating devices, The thermostat 230 may be attached di.rectly
¦ to the evaporator in order to determine when the evaporator has
¦ re~ched a temperature which will melt acc~mula-ted ice and frost
,., ¦ or othex types o~ sellsol~s which measure the amo~lnt of frost or
icc including the frost sensor itself may be utilized to produce
!, the termination signal. If a run off jumper 232 is not connected ¦
.,~ . ~ . I
~ I as shown, the defxost control switch 210 holds the refr.igeration
.~ 25 ¦ valve212 in the closed posi-tion to prev nt ilNmediate circulation o~
.,,~,, ! I .
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,,- . I , s
refrlgerant through the evaporator. At khis time, therefore~ the
evaporator is receiving neither heat throu~h the defrost valve
216 nor refrigerant thrcueh the valve 2127 and melted frost and
; I ice is given the opportunity to run off of the evaporator coils.
I At the end of a run-off period, the defrost control
!switch receives a defrost terminate signal from a defrost time
I llimiter 234. The time limiter in a preferred embodiment is a
settable solid state timer which is preset for a speci~ic period
lequivalent to the maximum period for a de~rost cycle. The limiter
! is driven by the same pulsed clocking signal which drives the
priority scanner 160 in the master control; however, it should
- be understood that other types of timers and different clocking
; signals could be used.
The limiter starts its tlming operation with the 5 :''
"~ 15 ,same signal that actuates the refrigeration and de-frost valves
¦212 and 216, and when the preset time period expires a reset
; Isignal is transmitted to the control switch 210 to re-open ! -~¦the refrigeration valve 212~ Thus~ when the run off-jumper
232- is not in place, the defrost valve is closed by the
Ithermostat 230 on the evaporator and the defrost control
switch ~10 holds the refrigeration valve closed until after
3 the time limiter 234 has run out. The interval bet~veen
jclosing of the defrost valve and re-opening of the refri-
geration valve allows melted frost to run off the evaporator
Icoils before refrigeration is resumed.
.. I
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, A second method of terminatin~ the de~rost operation
! occuxs when the run-o~f j~lmper 232 i5 installed. When the defrost
texminate signal :Exom the thermostat 230 unlatches the circuitry
214 and closes -the defrost valve 216, the de~rost termina-te signal~
is also transmitted directly to the control s~Yitch 210 and the
refrigeration valve 212 is opened at the same time. ThUS, there
is no run-off period With the jumper 232 installed, and re~rigera-
tion o~ the evaporator begins immediately upon closing o~ the
¦ de~rost valve.
~10 I A third method o~ terminating defrost occurs when the !
de~rost thermos-tat 230 is disconnected, oX not provided in the
system, or the time limiter runs out be~ore the thermostat sends
¦ a terminate signal. Under such circumstances; the de~rost time
limiter 234 rUn~ its ~Ull preset time and therea~ter resets the
~15 I control switch 210. ThUS, at the end of the timecl period, the ,~
I de~rost valve216 is closed and the re~rigeration valve 212 opens ! ~ ~:
¦ to begin a re~rigeration cycle.
I ' .
AL~RM SYSTEM
! . A tempexature rise thermostat 2~0 connected with the
¦ evaporator 30 and the individual control ~0 is provi~ed to detect
, abllormal increases in the evaporator temperature that arise from
: a ~ailure of the re~rigeration system. The thermostat is con-
¦' nected thiough an alarm locl~out delay circuit 2~2 to an alarm
! indicator 244 within the indiviclual control 40. The alal~ ¦
! indicator is also connected with a co~mon alarm an~ nciator 246
I .
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: 11
in the master control 38. If an abllorrnal and un~nticipated rise
I in temperature occurs in the evaporator 30, the thermostat 40
triggers the alarm indicator2 ~ to identify the evaporator as
¦ not properly ~unctioning. The alarm annunciator 2~6 which is
common to all of the evaporators in the re~rigeration system is
also sounded.
- Since the defrosting operation raises the temperature
¦ of the evaporator 30 well above the temperature that triggers
the alarm signal, it is necessary to lock out the alarm system
'10 during a de~rost cycle and fox a limited period thereafter while ¦ -
the temperature of the evaporator is lo~vered to its noxmal refrig-
eration level. The alarm lockout delay circuit 242 thus receives !
an actuating signal from the de~rost control switch 210 as soon
I as the de~rost cycle is initiated. In one form, the delay cir-
i c~it is a solid state -timer driven by the common clocIiin~ pulses ,
¦ applied to the time limitcr 23~ and the priority scannex 160.
¦ The delay circuit may be an adjustable solid state co~lnter which
; ! allows the loc~out period followiIlg defrost -to be selected.
. ~ .
SOLID STATE E~IBODI~IENT ¦
I Fig. 6 illustrates a solid state em~odiment o~ the
individual control 40 described in ~ig. 5 and the interconnections
with the master control 38.
The time and mode selection circuitry 200 in Fig. 6
~ is comprised o~ a plurality of patcll circuits or selector
;~5 ' switches 250, 252, 254, 256, 25~, an OR g~te 260 and a control
~ ~ gate 262. The switches receive timc si~nals from the decotlers
~ '~
-30-
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' 52 and 54, frost signals from the sensor 202 and discrete probing
¦¦ signals from the scanner 160 in the m~ster control. The switches
250, 252, 25~, and 256 have input contacts which are connected
with the twelve output texminals 90-112 of the 24-hour decoder 54
¦as shown and can be set to select one Ol more time signals for -.
j programming defrosting of the evaporator 30 ~Yhen a timed defrost
mode is desired. Thus, the evaporator can be set to deflost at
more than one time pe~ day. If a dernand mode is desired rather
ll than a timed mode, each of the switches 250, 252 and 25~ is
- 10 . connected to ground and the switch 256 is set on the contact
connected with the frost sensor 202 to receive frost signals.
, The switch 258 has contacts connected respectively with ~
the outputs 80-86 of the two-hour decoder 52 as well as one of thei
outputs of the priority scanner 160 in Fig. 2. It should be
lS j understood that the priority of the evaporator 30 is established
¦ by the output of the scanner connected with the input ter~inal
I of switch 258. If it is not desired to scan the evaporator 30
¦ and control 40 at all, then greater resolution of the programmed
I de~xost time may be had by connecting *he switcll 258 with one of
i20 i the output t~rminals for the two-hour decoder 52 t
¦ The control gate 262 is illustrated as a three-input
' NAND gate which provides a coincidence function. One of the
i inputs is connected with the OR ~ate 260, and receives time
~ , sigtnals or ~rost signals from the selector switches 250-256.
.. : I
j ~ second o~ the inputs is connectecl ~;ith the selcctor s~itch
¦ 258 and receives other time signals or pro~ing signals. The t
,~ '
~ , -31-
~' ' I
,
! ll~Z~79
¦, third input is normally held in the binary l-state or enabling
' condition b~ the po~er supply and resistor 136 (Fig. 2) in the t
mastex contxol, but is placed in the disabling condition or
binary 0-state by a tlefxost signal from any one of the othex
evaporatoxs 32, 34 in a de-rost cycle. Coincidence o~ the time,
frost or probing signal.s on the first and second inputs of
¦ control gate 262 when the enabling signal is present on the
third input causes a de~rost ac-tuating signal to be transmitted
by the gate through a NAND gate 26~ to -the de~rost control switch !
210. A disabling deirost signal on the third input.locks out
: ! opexation of the control gate so that any oF the timing, probing¦ or frost sensor signals received while anotler evaporator is in
a defrost cycle has no effect upon the control ~0. Thus, the
! control gate performs the ~unction o~ the defrost lockout cir-
~ cuit 206.
: I The deFrost ac~uating signal is transmit-ted through a
2-hour latch circuit co~nprised of the N~ND gates 264.and 266.
In a time mode, the actuatin~ signal ~hcn received by the gate
: j 26~ changes the ou$put of that gate to a l-sta-te and latches the I .
I output in that state through the NAND gate 266 until the time
~ I signal;~rom the OR ~ate 2~0 ~isappears at the end of a two-hour t
;: period. Since a hot gas de~rost operation can usually be com-
pleted substantially be~ore a t~:o-hour time signal would ~s-
appear from the output o~ OR ga-te 2G0, it would be possible, in
the absence o~ the t~o-hour la-tch circuit, tllat a repeat defrost-
¦ ing o era-tion woulù occur i~ ed ately upon tll3 term~ination o~
~1 1
!
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i
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', l!
a first defrostin~ operation. The l~tch circuitry ensures that
a defrost operation will not occur because the output of NAN~
' 264 is held in the l~state by the latch circuitry, and the
defrost control switch 210 is a solid state switch, such as a
I "D" type ~lip-flop ~ctuated only by the positive goln~ transition
i of an actuating signal received from the gate 264. Thus, by
latching the gate 264 the control s~itch 210 is ef~ectively dis-
~` i abled insofar as ~urther time signals are concerned.
; l The manual defrost button 222 is connecte~ directly to ,
~ the set texminal o~ the defrost S~Yi tch 210 and sets the switch
independently of clock signals or othe1 lockout circuitry. When : -
¦ set, a defrost cycle is carried out in a normal manner. ,
¦ Whenever the de~rost control switch 210 is actuated
~;i ¦ by either the de~rost button or a clock signal ~rom the control
-~ 15 gate 262, ths oppositely phased output terminals Q, Q change
¦! their xespective billary states. The Q-terminal is connected to
the defxost valve 216 by way of unlatching circuitry comprised
of N~ND gates 270, 272, 274. The output of the N~ND gate 270
, controls actuation of the valve through a resistor 276 connected
..
-20 to the base o~ a PNP power transistor 278. The ~ND gates 272
i
I . and 27~ haveinterconllected ~eedback and the outpu-t of the gate
f , ~2 is normally in the l-state enabling the ~ate 270. Thus, when ,
I the Q-terminal o~ the control s~Yi-tch 210 assumes the l-state,
; ~ the gate 270 places the transis-tor 27~ in the conductîYe state,
~25 and actuatcs the defrost valve 216 to apply hcat to the evaporator
.,', . Ii
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At the same time the Q terminal of the switch 210
assumes the 0-state and deactuates or closes the refrigerati~
Ivalve 212 throu~h a resistor 280 and NPN transistor 282. Thus,
a de~rosting cycle is initiated by the control switch 210 by open- !
ing the de~rost valve and'simultaneously closing the refrigeration
valve'. At the same time a defrost lockout signal is produced by the
terminal of switch 210 and the signal is transmitted to the master;
i~ control and ot~er individual controls thlough the isolation diode
0 302. ' '
I~ the mode switches 250-258 are in the timed mode,
that is, each o~ the switches is in a position responding to a
time signal, the control switch 210, rcfrigeration valve 212 and
defxost valve 216 are actuated in the same manner as described
above when the test button 22~ is pressed and held in a test
joperation. Pressing the test button 224 ~rounds the associated
¦input of a NAND gate 290 normally in the l-state due to the power ~
¦supply and resistor 292 and transmits a test signal such'as sho~vn ~ j
!through a diode 294 to the ma.ster control 38 and the other indivi-¦
;~0 ~dual controls ~2, 4~ in the xe~rigeration system. At the same
jtime, -~orward bias on the NPN transistor 296 through the base ¦
Iresistor 298 is removed which causes the capacitor 300 to discharge
- Ithrough resistors 306 and 308.
i The test si~nal causes the time clock 50 in $he master
¦control to be driven a-t an accelerated rate until the programmed
¦time o~ defrost ~or the control unit ~0 is reached. A-t this
i Ipoint, the control switch 210 is actuated to initiate a defrost
jcycle and produces a de~rost lockout si~nal ~rom the Q output
'
-3~-
J 1~3~6~
I
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1-
! which signal is tlansmitted to the master control and other
¦ individual controls 42, 44 through the isola-tion diode 302. Driv-
: ! ing the time cloc~ at the accelerated rate then ceases but the
~ defrost cycle initiated by the clocl~ continues until the test
~' 5 1~ button 224 is released.
hen the test button 224 is released, ground is res~ored
to the capacitor 300 throu~h the transistor 296 which alsc~ lower's
the input termina'l of N~ND gate 304 momentarily to the 0-state
while the capacitor 300 xecharges. The NAND gate 304 is momentar
I ily actuated which pulses the reset terminal o:E the control
I switch 210 to reset the s~vitch and the valve 212 and 216 for a
¦ refrigeration cycle. Thus, the test function terminates as soon a
the test button 224 is released. '
' The N~ND gate 290 serves khe -function o~ the clock lockl-'
` 15 I out circuit 208 in Fig. 5 when the other individual evaporator con
~ 'trols 42, 44 are tested and inhibits actuation of the control
¦ switch 210 in the event that programmed time'signals are recei~ed.
' I For example, when a test button in the indi~idual control 42 is
'` t actuated ancl the digital time cloc~ begins running a* an acceler-,
~ ated rate, the programmed time for individual control 40 could
' be reached be~ore the programmed time for individual control 42.
¦ In this case, when the progra~ned time signal in control 40 is
transmitted through the control gate 262 to the clocking terminal'
~ j T of the control switeh 210, the D or data terminal of the
... ,. I
1 s~Yitch is at the 0-state clue to the cloc~ setting signal applied ,
- I to the NAND gate 290. The binary state oI the data terminal is
transfe red to the Q terminal when the clocliing si~nnl is recei~e~
~''', ~ ~ ` - i
i
I
326'75~
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¦' by the T input. Thus, no change in the state o~ the Q and Q
outputs occurs even thou~h a clocking signal is received by
the switch, when some othex evaporatox is tested.
I The NAND gate 290 also per~orms the same lockout
¦ unction whenever the di~ital time clock 50 is manually set.
However, the NAND gate 290 does not disable the control switch ''
210-when the test button 224 is actuated because the test signal
is applied to the one terminal of the NAND gate 290 normally in
the l-state. Therefore, the gate 290 performs the operation of ¦ -
I the inhibit circuitry 226 in Fig. 5.
~` . j To terminate the de~rost operation wlth the aid of the
¦ de~rost terminate thermostat 230, a 0-state signal is transmit$ed~
froin the thermostat to the N~ND gate 27~ which in conjunction with
the NAND gate 272 ~unctions as a bi-stable ~lip-~lop. The 0-stat~
I~ signal causes the OutpLIts o~ gates 272 and 274 ~nd NA~D gate 270
j to chan~e and render transistor 27S nonconductive. The de~rost
~alve 216 consequently closes. Sillce the ~lip-~lop formed by -
~ ¦ gates 272 and 274 has no control over the re~rigeration valYe212 "
,, , the valve xemains closed assuming that the run o~f jumper 232 is
,~ 20 ! not installed. During the period in which both valves 212 and
¦ 216 are clo,sed, melted ice and ~rost is allowed to drip o~i the
e~aporator coîls.
, It will be observed that the Q output of control switch
210 is connected to the reset terminal o~ time limitex 234. The
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i limiter incl-ldes a resettable bin~ry countel 310 driven by the ~'
¦¦ clocking signals from tlle ~enerator 180 in Fig. 2. The Q output
of the control switch 210 holds the counter at its zero count
Il until the de~ro~t valve 216 is opened, and the re~rigeratiOn
5 li valve is closed. Clockillg pulses drive the binary counter throu~h-
out the defrosting operation to a predetermined count or
l j time which is adjusted or preset by a patch circuit 312 bet~een
.~ I the counter 310 and a three-input coincidence gate 3i4 in the
¦ limiter~ The patch cixcuit alld coincidence gate ef~ectively form
10 !~ a time decoder ~vhich produces a termination signal at the end of
a predetermined maximum deIrost period. The coincidence signal
activates the NAND gate 30~ and causes the control switch 210 to
¦I be reset to initial conditions ~hich xenders transistor 282 ¦
:~ . j conductive and opens the r~frigeration valve.212. Thus, between I 1
lS ! the time that the defrost terminate signal closes the de~rost 1,.
valve 216 and the time that the counter 234 runs out, melted ice
ij and frost fI'Om the evaporator coils is pexmitted to run o~f. ¦
¦~ Once the refri~er~tion valve lS opened, condensed re~rieerant s I
," ~ . , .
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; 1. . . . .
.. Il . I
/ i
~ ' 1, ' ' 1,
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11~ 113;~.i'79
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i de~ered to the evaporator 30 to l~csume the r~frigelation pro-
¦ cess.
! The second method o~ termillclting the defrost operation
¦ is carried out when the run of~ jumper 232 is installed as shown
I in phantom. With the jumper installed, the deIrost terminate
¦ signal actuates not only the unlatching circuit and deFrost valve
216 but also the reset gate 304. The control switch 210 is then jreset and the defxost valve ~6 is closed through NAND gate 270
j simultaneously with -the opening o~ the reErigeration valve 212.-
~ No run off period is permitted. - ¦
The third method of terminating the de~rost operation
is carried out wi-thout the aid of the thermostat 230 either be-
cause the thermostat is not included in the system or because
':".'
the time limiter 23 is selected to actuate the gate 304 ~nd
reset the control switch 210 before the de~rost terminate signal
¦ from the thelmostat is produced. As soon as the s~itch 210 is
¦ reset, the refrigelation valvc and defrost valve are opened
j and closed respectively. Thus, again, there is no run off.
~ The alarm lockout and delay circuitry ~42 in Fig. 5
j is comprised o~ an OR gate 320 connected with the control s~itch
210 and the temperature-rise thermostat 240, a binary counter 32Z
and another t'D" type flip-flop switch 324. During a refrigeratio~
cycle, *he temperature rise thermostat 240 normally permits a
binary l-state signal from the po-~er supply and resistor 330
~ 25 i to cxist at one input of the OR gate 320 ~.~hich t.hrough
`~ ¦ resistor 3~S blocks conduction oi the PNP transistor 3~G and
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11 !
326'7~
~revents activation of the alarm indicator 244 and co~on ala~n
246. When the evaporator 30 associated with the control 40 is
defrosting, a temperature rise would remove the blocking
signal and cause an alarm but the alarm indicator is effectively
disabled by the delay circuitxy during defrost and a brief
period thereafter.
One input of the OR gate 320 is connected to the Q-
terminal of the control switch 210. When the Q-terminal
assumes the l-state as a defrost operation is started, con-
duction of transistor 324 is blocked and thus the alarmindicator 244 will not produce a temperature rise alarm signal
nor actuate the common alarm 246.
At the end of a defrost cycle when the refrigeration
valve is again opened, the evaporator 30 will still be at an
excessively high temperature which could generate the alarm
signal. To continue blocking of the alarm signal, the flip-
' flop 324 is clocked by the positive-going transition of the Q
'. output of switch 210 when the refrigeration valve 212 is opened.
The flip-flop 324 then transmits a binary l-state signal to OR
gate 320 which signal replaces the blocking signal previously
: received from the control switch 210. At the same time, the Q
output of the flip-flop resets the binary timer or counter 322,
and the standard clocking pulses count out a predetermined time
interval within which the evaporator should have been lowered
to its normal refrigeration temperature. As illustrated, the
counter ...
39~
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ha- s veral outputs permitting adjustment or selection of the
time interval for reaching the refrigeration temperature by means
of a switch 332, One of the outputs is manually selected or
connected to the reset termillal o-f the flip--flop 324 so that at
the expiration of the selected time interval, the flip-flop 324 -
is reset, and the blocking si~nal is removed from the input of OR
gate 320. By the elld of the timed interval the evaporator
Ishould have been lowered to the normal re-frigeration temperature,
¦and the temperature signal -from the thermosta$ 240 should have -
Ireturned to its l-state to continue to hold the transistor 326 in
its nonconductive state and block the alarm. At any subsequent
¦time when the temperat~lre of the evaporator rises, the blocking
jsignal is removed and the transistor 326 conducts and actuates
¦the alarm indicator 234 and common alarm 246.
~15 ¦ Fig. 7 illustrates a d.c. power supply means that is
prefera~ly utilized for energizing the master control 3~J the
individual controls 40, 42, 44 and the digital time clock 50 from ' -
60 cycle utility power. It will be understood that in the event
,o~ a power ~ailure and re-establishment of power, the digital
Iclock witho~lt an internal nlemory resumes its co-lntin~ or timing
,function at an unpredictable time. Also many of the solid state
components s~lch as the decoders 52, 54 lose track oi their se- ~
Iquencing. ~Yhen certain or all of the evaporators are scheduled . -
¦!~or timed defrosting, it is conceivable that UpOII restoration of
power the eVapOratOlS in need o-f de-frost prior to the failure ~ould
Inot be reached for an inordinately long time because the solid
'state components cannot per-form a memory function.
. ~ _~o~
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1 ~13~679
IFor this reason, a d.c. power supply 340 for the
electrical system is augmented by an au~iliary battery 350.
Since only the eo-lnting circuits in the time clock and other
¦selected digital components in the master control 38 and indi~
¦dual controls 40, 42, 44 are eritical to the memory function,
land because all of the components could readily drain the battery, !
: ~more than ttvo voltage terminals are provided. There is at least
one terminal 342 of one polarity and two terminals 344 and 346 of
Ithe opposite polarity energized by the power supply ~vhen utility
¦power is on. The auxiliary battery 350 or other emergency po~er
souree is eonnected bet~veen the terminals 342 and 344 and the
elock 50 and other eritical components are connected with these
terminals as indicated by the re-ferenee numerals in box 348.
;` The remaining eomponents possibly including the time display of
the eloek eonnect with terminals 342 and 3~6. The blocking
diode 354 isolates the battery ~rom such remaining components so
they are not energized during a power outage. The diocle 352
<
proteets the battery from being overeharged by the power supply
and proteets the system components against inadvertent polarity
reversal when the battery is installed. The diode 356 serves a
resistive function and matches the diode 354 so that the po~ver
supply voltage applied to the components conneeted ~ith terminal
346 is the same as the voltage applied to components conneeted
with terminal 344. Thus the battery 350 and the connected
eomponents provide a memory for the various timing lunc-
¦tions a ensure thRt upon the restoration oF utility
_~_
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i~ 2~
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, power, the defrosting sequence ~vill resume ~rom the point at
which po~ver was lost.
l In sum~ary, the re~rigeration system illustrated in
¦¦ Fig~ 1 has independently de~rosted evaporators whose operation
i lS regulated by a master control 3S and a plurality of individual
controls ~0, ~2J 44 respectively. In a timed mode of operation,
¦ time signals arederived from a digital time clock and in a
demand mode the indi~idual contxols xespond to command signals
from ~rost sensors. Testing of the individual controls is per-
~10 ¦ ~ormed by driving the time clock at an accelerated rate to the
programmed defrosting time. After every testing, time-set$ing-
and defrostin~ opexation, the individu~ controls and their
I associated evaporators may be scanned in order o~ priority to
j detect which evapora-tor is the next ullit in need o~ de~rost.
I The entire control system can be embodied in solid state form for
~¦ high reliability and compact installation.
I While the present invention has been described in a ¦
pre~erred embodiment, it will be understood that numerous modi~
~ cations and substitutions can be made without departing ~rom the
i spirit of the invention. Most clearly, although the digital
clock decoding technique provides a convenient device ~or ob- -
~ taining widely spaced time signals ~or various de~rostin~ opera-
I tions, the timing signals can also be obtained from digital or
~ analog timing devices in othex ways. The priority scanning
l, techn que enables a clcar system of priorities to beestablished
,1, ' I
for the evaporators in various refrigeration cabinets, but
no scanning is necessary and other scanning devices such
as shown and described in U. S. Patent 4,151,722 referenced
above can be used instead. The fast clocking feature for
testing is integrated in the control system in a convenient
manner when the testing device is a digital clock but it
can also be utilized with other timing devices. Naturally,
the scanning and testing functions may exist together or
separately in a refrigeration system. While the individual
defrost control and the master control have been illustrated
in a solid state form, it should be understood that the
general functions of the controls can be accomplished with
other digital or analog equipment. Accordingly, the present
invention has been described in several forms by way of
illustration rather than limitation.
-43-
